This invention relates generally to the processing of soy-derived materials for use in various food products, especially cultured soy products. More particularly, the invention relates to a method of deflavoring soy materials in order to make them acceptable in a wide range of foods, including cultured soy products.
In recent years, soy proteins have become widely used in food products, for the health benefits to be obtained from their use. In some applications, the taste of the soy materials is not objectionable. However, in some uses, such as dairy analog products, beverages and the like, the flavors found in soy materials may prevent their ready acceptance by the consumer. Thus, in order to extend the uses of soy materials, the present inventors wanted to find a method of reducing the flavor components of soy materials. However, it was not evident that methods which had been used previously to remove flavor components from other organic materials would be successful in the treating of soy materials. Organic materials, since they have complex compositions, must be tested to determine whether any given method of treating them will be satisfactory.
One example of previously employed methods to purify organic materials is found in U.S. Pat. No. 4,477,480, in which the patentees show that starch can be treated with an alkali to remove objectionable flavor components. In a commonly assigned patent, U.S. Pat. No. 4,761,186, ultrafiltration is used to purify starch. In both cases, flavor components are removed from the starch, in the '480 patent by solubilizing the flavor components so that they can be washed out of the relatively insoluble starch. In the '186 patent, ultrafiltration was used to remove the flavor components as permeate, while the insoluble starch remained in an aqueous slurry. By contrast, the present invention separates flavor components from soluble high molecular weight soy proteins.
There are many articles and patents which relate to processing soy materials in order to recover the protein content and which at the same time reduce the flavor compounds to make the proteins more acceptable in food products. However, these previous disclosures were not specifically directed to removal of flavoring compounds and recovering as much of the protein as possible. One example is U.S. Pat. No. 4,420,425 in which protein components of soy are solubilized at a pH of 7 to 11, preferably about 8 and, after ultrafiltration through a membrane having a molecular weight cut off above 70,000, are recovered by spray drying the retained soy proteins. In variants, only a portion of the protein is solubilized at lower pH values and subjected to ultrafiltration with a membrane having a cutoff preferably above 100,000 molecular weight, the product was found to have improved color and flavor. A higher cutoff valve would be expected to result in a loss of valuable proteins. In another patent, U.S. Pat. No. 5,658,714, a soy flour slurry is pH-adjusted to the range of 7 to 10 to solubilize proteins, which are then passed through an ultrafiltration membrane and phytate and aluminum are retained, presumably as solids. While the molecular weight cutoff of the membrane was not given, it is assumed that the pore size was large in order to be able to pass the soluble proteins. Both of these patents contain extensive discussions of the efforts of others in the processing of soy materials; neither teaches or suggests the control of pH during the ultrafiltration process.
In a group of related patents, Mead Johnson Company disclosed processes for solubilizing soy proteins by raising the pH of an aqueous solution of soy materials and recovering the proteins which are said to have a bland taste. The processes are principally directed to concentrating proteins rather than removing flavor compounds. In U.S. Pat. No. 3,995,071, the pH was increased to 10.1 to 14 (preferably 11 to 12) to solubilize soy proteins, after which the pH was lowered to about 6 to 10 and ultrafiltration with a membrane having a molecular weight cutoff of 10,000 to 50,000 Daltons was used to retain the proteins while discarding carbohydrates and minerals. In U.S. Pat. No. 4,072,670, emphasis was placed on removing phytates and phytic acid by solubilizing proteins at a pH of 10.6 to 14 and a temperature of 10 to 50° C. to make the phytates and phytic acid insoluble, then separating them and finally acidifying the solution to a pH of about 4 to 5 to precipitate the soy proteins. In U.S. Pat. No. 4,091,120 soy proteins were solubilized at a pH less than 10, preferably 7 to 9 and ultrafiltration was used to separate the proteins as retentate, while passing carbohydrates as permeate. These patent do not teach or suggest control of the pH during the ultrafiltration process.
The present inventors wanted to remove compounds in soy materials which contribute color and flavor and which interfere with the use of soy in certain food products such as beverages, dairy analogs, and the like. They have found that soy-derived materials can be treated successfully using the process to be described below, recovering substantially all of the proteins and rejecting the compounds which cause undesirable color and flavor. Moreover, by controlling the pH within the range of about 9 to about 12 during the ultrafiltration process, deflavored soy materials having improved functional properties can be obtained. Thus, the product is suitable for many food products.